The present invention relates generally to internal combustion engines, and more particularly, to a combustion chamber design and method of operating an internal combustion engine, and specifically to a diesel locomotive engine and method of operating the same in compliance with the United States Environmental Protection Agency Tier-2 Emissions Standards.
It is well known to use a fuel injected diesel internal combustion engine as a power source for a locomotive. As a piston moves upward within a cylinder of a diesel engine, the air within the cylinder is compressed and heated. Fuel is injected into the combustion chamber as the piston nears its top dead center position. The fuel combusts with the compressed air, thereby providing energy for driving the engine and locomotive. There are many variables affecting the performance of a diesel engine, including the compression ratio, size of intake and exhaust valve openings, timing and duration of fuel injection, geometry of the combustion chamber, and peak temperature of the combustion gasses. In order to promote efficient operation of a diesel engine, it is known to optimize the size of both the intake and exhaust valve openings in order to reduce the pumping loop losses associated with the movement of the combustion and exhaust air. Because the cylinder wall is typically at a lower temperature than the piston top surface, it is also known to avoid the direct impingement of the injected fuel onto the cylinder wall because such fuel will not be completely oxidized during the combustion process. In order the minimize the loss of combustion heat through the cylinder wall and to minimize the amount of fuel that is impinged directly onto the cylinder wall, it is known to form a combustion chamber depression in the top surface of the piston in an area removed from the edges of the piston. One such design is illustrated in U.S. Pat. No. Re. 34,139 dated Dec. 8, 1992. An alternative design for maintaining the combustion gasses proximate the center of the piston is illustrated in U.S. Pat. No. 5,878,712 issued on Mar. 9, 1999. In this design a domed piston is provided with a dished depression which directs the combustion gasses away from the cylinder walls.
The United States Environmental Protection Agency has issued regulations directed to reducing the emissions from diesel locomotive engines. The Tier-2 Emissions Standards become effective on Jan. 1, 2005, and will require a significant reduction in the production of the oxides of nitrogen in diesel locomotive engines. While it is known to reduce the peak firing temperature in the combustion chamber of an internal combustion engine in order to reduce the production of the oxides of nitrogen, such a reduction in peak combustion temperature is known to result in a reduction in the efficiency of the engine operation.